Control circuitry and method for vibratory feeder

ABSTRACT

A material dispensing apparatus including drive structure for driving a feeder bowl is disclosed. A control circuit for controlling the drive includes a Hall effect amplitude sensing transducer for monitoring the magnitude of bowl vibrations and a braking circuit for controlling the damping of vibratory motion after the requisite amount of material has been fed from the feeder bowl. The braking circuit selectively reverses the current flow through a drive coil which comprises a portion of the drive circuitry of the apparatus. This current reversal disrupts the rhythm of forced oscillations which feed material from the bowl and causes bowl motion to be damped.

This is a continuation of application Ser. No. 053,104 filed June 28,1979 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to a vibratory feed mechanism, and inparticular, to a feed mechanism which includes an improved amplitudesensing and damping method and apparatus.

2. Prior Art

Systems including vibratory feeder bowls are known for feeding streamsof parts or other particulate material. Such a system typically includesa feeder bowl coupled to a stationary base by leaf springs. Relativemovement of the bowl and base causes parts within the bowl to move up anincline spiral path and fall into an accumulating container.

In a typical system parts segregated by a vibratory feeder bowl areeither weighed or counted to collect a batch of a desired size. Once thebatch is complete, the parts are either moved away from the feeder by aconveyor system or are dumped from a first accumulator to a secondreceptacle and then removed.

As an example, three vibratory feeder mechanisms might be arranged inparallel. A first mechanism would deposit a desired number of bolts ontoa conveyor. The second and third feeder mechanisms would send anidentical number of nuts and washers to the conveyor to be added to thebolts provided by the first mechanism. In this way a like number ofnuts, bolts and washers will be fed from individual vibratory mechanismsand combined to form a batch each containing the proper number of parts.Typically they are then fed to a packaging station.

As the parts are dispensed from the feeder bowl it is desirable that theamplitude of vibration of the feeder mechanism remain approximatelyconstant. It is known that the amplitude of bowl vibration depends uponthe mass of materials within the bowl. As the total mass of the bowlcontents decreases, a reduction in driving power is necessary tomaintain a given amplitude of vibration for the bowl. As the amount ofbowl contents increases, the amplitude of vibration will diminish for agiven driving power. Proposals have been made to sense the amplitude ofvibration of the driven bowl and compensate for changes in the bowl byvarying the power acting upon the bowl. The objective of such proposalsis to maintain relatively constant vibratory amplitude while parts arebeing fed to an accumulator.

Prior amplitude sensing techniques have employed inductive elementsmounted to the feeder in close relation to a magnet which vibrates withthe feeder bowl. As the bowl vibrates, thereby feeding parts in the bowlto a conveyor or packaging station, relative motion between the magnetand an inductor produces an oscillating electrical signal whosemagnitude depends upon the amplitude of vibration. This signal has beenused to sense the amplitude and control the driving power to the bowl.At small amplitudes of vibration, however, the signal generated in thismanner was too small to provide an adequate control signal.

A small amplitude of oscillation is particularly useful in small batchprocessing where a large amplitude is inefficient since the feeder iscontinually being started and stopped. Thus, prior art amplitude sensingtechniques has been somewhat inadequate when controlling the feeding ofsmall batches of parts.

Another problem with prior vibratory bowl feeders is that they arecharacterized by inefficient batch feed through due to problemsencountered stopping vibrations when a batch has been completed. Priorsystems count the number or weigh the mass of units fed from the bowland seek to terminate the drive power to the bowl when the proper numberor weight of units has been fed. A problem has been that when the powerhas been removed from the driving circuitry, the bowl continues tooscillate or vibrate for a finite period of time due to its inertia andthe restoring action of its coupling leaf springs. As the bowl continuesto vibrate, the units within the bowl may continue to be fed from it andaccumulate in the container. Thus undamped oscillation after powertermination may send more than the requisite number of units into anaccumulator or container.

Expressed another way, one problem has been that prior feeders tend toover feed. Various expedients have been used to compensate for the overfeed problem but the problem itself has continued.

Some prior art systems have dealt with the over feed problem byincluding a diverter into which the excess parts were fed after forcedbowl vibrations were terminated. The excess parts were accumulated andperiodically emptied back into the vibratory feeder bowl. These divertersystems were inefficient since the excess parts must be continuallyreturned to the vibratory apparatus and they exhibited othershortcomings. One such shortcoming was repeated recycling could causeexcessive wear with some parts and another shortcoming was the diverterwould not neccessarily provide the precise flow cut off desired.

A second technique for dealing with the over feed problem was to slowdown the oscillations as the requisite number of parts was neared duringthe feed process. This slowing down of the vibration as the correct partnumber was neared resulted in a reduced through put for the system.Instead of operating at maximum efficiency for the full cycle for agiven batch, the oscillations were slowed as the proper count wasneared. This technique also required control circuitry to monitor thenumber of parts in the accumulator and compare that number with thefinal count to be achieved.

SUMMARY OF THE INVENTION

The present invention obviates the need for a diverter or other type ofover feed compensation and includes an improved amplitude of oscillationsensing technique. The result of these innovations is a maximum throughput of parts. A stopping or braking mechanism of increased efficiency isprovided which applies a damping force to the feeder's vibratory bowl.The damping force causes the bowl to stop vibrating more rapidly thanprior art systems. The bowl can be driven close to maximum speed untilthe proper article count or weight has been accumulated. An increase inefficiency of the order of 40 to 50% can be achieved when articlebatches of small quantity are fed by the system. An amplitude controlsignal is generated which results in an adequate control signal at allamplitudes of oscillation and in particular for low level oscillationused in small batch feeding.

A typical dispensing apparatus embodying the present invention includesa drive means for vibrating a bowl mechanism which in turn impartsmotions to a unit or part to be counted. Apparatus of the presentinvention further includes a control circuit which carefully monitorsthe amplitude of oscillation and applies a braking force when thevibrating power is turned off.

More particularly, the control circuit includes a speed control circuitfor controlling oscillation of the bowl. An amplitude sensing circuitwhich comprises a Hall effect transducer is included for monitoring thebowl oscillations and which in conjunction with a control circuit signalmaintains oscillation amplitudes in a preferred range. A power circuitreceives a control signal from the amplitude sensing circuit andproduces a driving signal to a bowl coil. Energization andde-energization of this bowl coil produces movement of the vibratorybowl due to electromagnetic interaction between a stationary and movingportion of an electro-magnetic system.

The control circuit also includes a braking circuit for reversing thecurrent within the power circuit and thereby reversing the direction ofoscillation inducing force applied to the bowl. This current reversalachieves a rapid braking of the vibrating bowl mechanism and therebyminimizes the over feed problem.

In a preferred embodiment, the braking circuit sends a timed brakingsignal to the power circuitry. This signal causes the bowl to be drivenbut in a timing sequence which disrupts the original oscillations. Thebraking circuitry further includes control circuitry which is used tofine tune the braking circuit to provide the braking signal to the bowlmechanism for only a certain time period.

The power circuit of the preferred embodiment includes controlledrectifiers for sending power signals to the bowl coil. A gating signalallows current to flow in these controlled rectifiers in response tocontrol signals from the speed control and braking circuits. When thebowl is driven during normal feed operation, a first controlledrectifier is periodically rendered conductive in response to signalsfrom the speed control circuit. When controlled braking is to beapplied, a second controlled rectifier in the power circuit is renderedconductive by an input from the braking circuit.

From the above it is apparent that one important feature and object ofthe present invention is to provide a damping or stopping signal to adriven vibratory feeder mechanism. In this way a more efficient countingmechanism is provided without the use of diverter or other excess unitcompensation techniques. The system vibrates at a constant frequency ofoscillation throughout its batch processing and is rapidly stopped whena batch of parts has been dispensed.

A further objective is an amplitude sensing circuit which accuratelytransmits amplitude data to the power circuit. This improved amplitudesensing is more accurately representative of the amplitude than priorart amplitude sensing techniques. These and other features and objectsof the invention will be better understood when considered inconjunction with the detailed description of the invention and theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of material handling apparatus embodying thepresent invention.

FIG. 2 is a top plan view of a vibratory feeder bowl.

FIG. 3 is a side plan view of the bowl illustrated in FIG. 2.

FIG. 4 is a side view depicting a mounting mechanism for the feederbowl.

FIG. 5 is a top plan view of the mechanism of FIG. 4.

FIG. 6 is a schematic of a control circuit for controlling the vibrationof the feeder bowl.

FIG. 7 is a more detailed schematic of the control circuit shown in FIG.6.

FIGS. 8A-8E show voltage waveforms at certain locations of the controlcircuit of FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a material dispensing apparatus using the preferredembodiment of the present invention is indicated generally by thenumeral 10. The apparatus 10 is operative to dispense articles, such aspills, washers, screws, or other small items into a container 12positioned next to the article handling apparatus 10.

The apparatus 10 includes a base structure 14 which supports a supplyhopper 16, and a vibratory feeder 18. The vibratory feeder 18 includes afeeder hopper or bowl 20 which deposits the units into the container 12.In operation, articles to be dispensed are loaded into the supply hopper16. The material dispensing apparatus then feeds controlled amounts ofarticles from the supply hopper 16 into the feeder 18. Vibratory motionof the feeder causes the articles to move from the feeder 18 into theaccumulator bucket or container 12. A limit switch assembly (not shown)maintains a predetermined amount of articles in the feeder 18 bycontrolling article movement from the supply 16 to the feeder 18.

The operation of the vibratory feeder can be controlled by an externalsignal from a counting unit 22. This signal will automatically controlthe dispensing of a predetermined amount or weight of articles into theaccumulator or container 12. After the required number of articles havebeen accumulated, the article dispensing apparatus 18 is turned off andmotion ended by means of the braking system embodied by the presentinvention.

Further details of a preferred vibratory accumulator unit as embodied bythe present invention can be found in U.S. Pat. No. 4,095,723, columns11, et. seq. which has been assigned to Automated Packaging Systems,Inc., the assignee of the present invention. This patent is specificallyincorporated by reference.

Referring now specifically to FIGS. 2-5, it is shown how the presentapparatus produces a vibratory movement to propel articles to beaccumulated along an spiral path in the bowl 20. More specifically,FIGS. 2 and 3 depict a vibratory feeder bowl 20 used for accumulatingthe parts to be counted once they are dumped from the feeder hopper 16.The parts are deposited in the bowl 20 and are caused to vibrate in aspiral path 24 until they reach the end of that path and are dumped fromthe vibratory bowl into the container 12. As seen in FIGS. 2 and 3 thevibratory bowl includes 4 flange elements 26 spaced at well definedlocations about the periphery of the feeder bowl. Each of these flangesincludes a threaded aperture 28 for receiving a connector which mountsthe vibrating bowl to an oscillating arm 44 (see FIGS. 4 and 5). In thisway, the vibratory bowl is suspended from the arms and, as will be seenwith reference to FIGS. 4 and 5, can be caused to oscillate to createmovement in the parts along the bowl's path 24.

Referring now to FIGS. 4 and 5, apparatus for oscillating the bowl isreferred to generally by reference numeral 40. This apparatus 40includes a massive supporting frame element 42 and a much lightersuspended element 43 including the arms 44 which extend generallyradially. The radially extending arms 44 include apertures which alignwith the apertures 28 in the flanges 26. Bolts, now shown, threaded intothe apertures 28 join the vibratory bowl with the radially extendingarms. The element 42 is suspended from the frame of the dispenser 10 bybolts 45 which thread into apertures in the frame element 42.

The suspended element 43 is suspended from the support element 42 bymeans of flexible leaf springs 46. As seen in FIG. 4, the leaf springsare attached to the support element 42 and suspended element 43 by meansof suitable connectors which in a preferred embodiment comprise athreaded bolt arrangement. The leaf springs 46 are angled with respectto the vertical in such a way that relative vertical motion between theradially extending arms 44 and the support element 42 will produce acircular oscillatory movement of the radially extending arms and theattached bowl.

Relative vertical motion between the support element 42 and the arms 44is achieved by means of an electromagnetic motor which utilizesconventional I and E laminations. The E laminations are mounted to thesupporting element and the I laminations to the radially extending arms.Energization of the E laminations causes a relative motion due to thechanging flux which energization produces. This flux interacts with theI laminations causing electromagnetic forces to be created between thetwo halves of the motor. These forces cause the radially extending armsto move vertically relative to the supporting element 42. This motion iscaused by the attraction of the I laminations to the field produced inthe E laminations.

Due to the angled mounting of the leaf springs 46, the vertical movementcaused by the electromagnetic interaction becomes a combined, relativelyslow, circular and vertical movement. When the magnet is deenergized,energy stored in the springs rather suddenly drives the bowl down and inthe opposite circular direction. Inertia of parts along the spiral bowlramp causes them to "climb" the ramp when the bowl is spring driven.This climbing causes the parts located within the bowl to move along thespiral bowl ramp and drop into the accumulating container shown in FIG.1.

During normal operation, oscillatory forces are applied to the bowl byalternate energization of the electromagnet. During the energization,current passes through a bowl coil 112 which wraps around the Elaminations of the magnet. The resultant electromagnetic force betweenthe I and E laminations reduces the distance between the base and radialarms. When current is removed from the bowl coil, the restoring actionof gravity and the leaf springs increase the gap between the base andarms. The cyclical energization and de-energization of the coil resultsin up and down oscillatory movement which inputs spiralling oscillationsto the bowl.

The bowl oscillations are controlled by a circuit 110 schematicallyillustrated in FIG. 6. One aspect of this circuit is the modulation ofthe amplitude of oscillation response to the weight of parts carried bythe vibratory bowl. When the bowl is relatively full, more power must besupplied to the electromagnetic motor to achieve the same amplitude ofvibration. A second aspect of the disclosed circuit is to provide abraking signal to the electromagnetic motor when an appropriate numberof parts have been dispensed. Were it not for this braking signal, thevibratory bowl would continue to oscillate with a natural undampedfrequency which would cause excess parts to be dispensed. This cause ofinaccuracy has substantially been eliminated by means of the unique andnovel braking technique.

The control circuit comprises a power circuit 120 which allows currentto flow through a bowl coil 112. The coil 112 is driven by a source ofenergy 113 which in one embodiment comprises a 120 volt alternatingcurrent source of 60 cycles per second. Since the blow coil 112 wrapsaround the magnet's E laminations, energization and de-energization ofthe coil causes the bowl 20 to vibrate due to the mechanical structureof the bowl support. As described hereinafter the power circuit 120controls the timing and direction of current flow through this bowlcoil.

The control circuit 110 further includes a speed control circuit 118, anamplitude sensing circuit 116, and a braking circuit 114 which incombination control energization of the bowl coil 112 through operationof a power circuit 120. The amplitude sensing circuit 116 and speedcontrol circuit 118 are connected in series and generate an output 170proportional to both a desired speed of operation and the actualamplitude of vibration of the bowl feeder. This signal is compared to asawtooth voltage signal by a comparator 150 which produces an input 144to the power circuit. The status of this input 144 determines the amountof power transmitted through the bowl coil 112 by the power circuit 120.The amplitude sensing circuit 116 includes a Hall magnetic transducer122 (see FIG. 7) which provides an oscillating signal proportional tothe amplitude of oscillation imparted to the bowl mechanism. The Halltransducer 122 also receives a signal from the speed control circuitwhich modulates the output from the amplitude sensing circuit to thecomparator 150. In this way, a feed back signal is generated which isdependent on both the amplitude of feeder oscillation and to a desiredspeed control signal from the speed control circuit.

The comparator 150 selectively renders conductive a switching means suchas a silicon control rectifier 130 (See FIG. 7) within the powercircuit. When the silicon control rectifier is rendered conductive, itallows the alternating current source 113 to drive the bowl coil 112 fora controlled time period. The control from the speed control circuit ismodified in response to the amplitude of vibration as sensed by the Halleffect transducer 122. As a result, a combined speed and amplitudecontrol technique is achieved for controlling the amount of power sentto the bowl coil 112.

The braking circuit deactivates signals from the comparator 150 bycontrolling a second input 146 to the power circuit 120. When a signalvoltage input to the braking circuit drops in response to a counter orswitch, the driven oscillation of the bowl is terminated. To dampcontinuing oscillations, the braking circuit produces a signal 148 whichis sent to the power circuit 120 causing alternating current to passthrough the bowl coil 112 but in a direction opposite to the directionof current flow during normal bowl oscillation. This reversing of bowlcoil current flow causes the bowl to be damped much more quickly than itwould if the power were merely removed from the coil. The reversecurrent signal is maintained for enough oscillations to damp the bowlmechanism but to not overdrive the mechanism in an opposite direction.The correct timing of this damping function is achieved via a tuning ofcomponents within the braking circuit 114.

A detailed schematic of the control circuit is illustrated in FIG. 7.Unless otherwise noted, all resistors are 1/4 watt resistors and allcapacitors are indicated in micro farads. Many of the elements withinthe circuitry are chosen for convenience but it should be appreciated tothose skilled in the art that certain design modifications could be madein the resistor or capacitor values without departing from the spirit ofthe invention.

As seen in FIG. 7, current flow through the coil 112 is controlled bythe power circuit 120 which includes two silicon control rectifiers 130,132. Depending on the conduction states of these two rectifiers, currentcan flow through the bowl from the 120 volt source in one of twodirections. During normal vibratory operation (i.e., when parts are tobe moved along the spiral ramp) a drive SCR 130 will allow conductionthrough the bowl in one direction. The other SCR 132, which will bereferred to as a braking SCR, will be rendered nonconductive so the bowlcoil will be energized during only a maximum of one half the alternatingcurrent cycle. During the half cycle the drive SCR may not conduct, thebowl will be driven in an opposed direction by the combined action ofthe leaf springs and gravity as noted previously.

When the requisite number of parts have been accumulated or the properweight of parts dispensed, the drive SCR 130 is rendered nonconductiveand the brake SCR 132 is rendered conductive for a brief period of timeto dynamically brake the bowl by allowing a back current to flow throughthe bowl coil in a direction opposite to its part feed flow. This backcurrent disrupts the rhythm of oscillations produced by action of thedrive SCR 130 and quickly brakes the bowl. No excess units or parts aredispensed by continued vibration of the bowl and unlike some prior artsystems during the bowl drive portion uniform frequency and amplitude ofbowl oscillation is maintained.

Gating inputs 134,136 to the two SCR's 130, 132 are respectivelyconnected to a pair of optically coupled SCR's 138, 140. When theseoptically coupled SCR's conduct, gating signals are sent to the SCR's130, 132. This connection is achieved through filter circuits 141 whichsuppress transient signals from reaching the SCR gates 134, 136. Each ofthe optically coupled SCR's provides a signal to its connected one ofthe gates 134, 136 in response to the voltage on three inputs 144, 146,148 to the power circuit 120. The relative size of the signals on thesethree inputs is controlled by operation of the speed control 118,amplitude sensing 116, and brake control 114 circuits. These controlcircuits will be described in detail but it should be clear from theschematic of the power circuit that one optically coupled SCR 138 willconduct whenever the input 144 is greater than the second input 146 andthat the second optically coupled SCR 140 will conduct and thereforeturn on the brake SCR 132 whenever the second input 146 is greater thanthe third input 148. It is control of the three inputs which determinehow the vibratory bowl is driven and damped.

As seen in FIG. 7, the voltage levels at the three inputs 144, 146, 148are respectively controlled by the output of three amplifiers 150, 152,154. Each of these amplifiers is configured to operate as a comparatorin that the output of each comparator is dependent upon the relativesize of its two inputs. The inputs to each of the three amplifiers orcomparators 150, 152, and 154 change in response of operation of thethree control circuits 114, 116, 118.

One midpoint amplifier 152 transmits an input 146 midway between the twooptically coupled SCR's 138, 140. During normal powered operation of thevibratory bowl, this input 146 is maintained at a low or groundpotential. This state is achieved through control of the amplifier's twoinputs 158, 160. A first input 158 is maintained at a reference voltageof about 5 volts by a voltage divider 162 and a 10 volt power source163. A second input 160 is maintained at an approximately 10 volt leveldue to connection to a second voltage divider 164 and a 12 volt controlvoltage 119. During normal operation of the vibratory feeder system, aset up switch is in a closed position. This enables the 12 volt controlsource to maintain the input 160 to the midpoint amplifier 151 at avalue of approximately 10 volts. When this input is compared to the 5volt input on the other input 158, a low or ground output 146 is sentbetween the two optically coupled SCR's 138, 140.

When the control voltage 119 drops below 5 volts, the forced vibrationof the bowl is stopped due to the change in output by the midpointamplifier 152. When the input 160 is compared to the positive 5 voltvoltage on the other input 158, the output 146 changes from its lowground state to its high state. In this configuration, no current maypass through the optically coupled SCR 138 which as a result sends nogating signals to the bowl drive SCR 130. Thus, when the control voltage119 is low the bowl drive SCR 130 is maintained in a nonconducting stateand the bowl drive vibrations are removed.

When the control voltage 119 is high, the optically coupled SCR 138 mayor may not conduct depending on the state of a second input 144 to thepower circuit. If the input 146 is in a low state, the optically coupledSCR 138 conducts so long as the input 144 from the first or drive bowlcomparator 150 is in a high or positive state. In this configuration,power will flow through the optically coupled SCR 138 sending a gatingsignal to the drive bowl SCR 130.

The comparator 150 has two inputs 168, 170 whose voltage dictateswhether the output 144 is in a high or low state. One input 168 to thecomparator 150 is a reference signal and is a sawtoothed waveform. Aconventional 120 volt alternating current input 113 is shaped into asawtoothed waveform by a sawtooth generator 173 to form this sawtoothwaveform input 168.

A second input 170 to the comparator 150 is generated by the amplitudesensing circuit 116. This circuit comprises a Hall effect transducer122, a differential amplifier 172, a comparator 174, and an intergratingcircuit 176.

The Hall effect transducer 122 has two outputs 180, 181 attached to thedifferential amplifier 172. The voltage difference between the two Halleffect outputs is proportional to a product of a control current flowingthrough the device and to a magnetic field component normal to an activeregion on the Hall effect transducer. Since the output from the Halldevice is dependent on two variables, it can be utilized as both a speedcontrol and amplitude sensing device. The current through the Halldevice is modified to affect a speed control and mounted to thevibratory feeder in close proximity to a magnet to achieve an amplitudesensing capacity.

As seen in FIG. 4 the Hall sensor is attached to the base support 42 inclose proximity to a magnet 179. Bowl oscillations bring the magnetcloser to the Hall transducer, thereby increasing the magnetic fluximpinging upon the transducer surface. Since the voltage of the twooutputs 180, 181 is dependent upon the magnetic field componentimpinging upon this surface, the amplitude of bowl vibrations isreflected in the voltage appearing at the two inputs to the differentialamplifier 172.

The speed control circuit 118 is also electrically connected to the Halltransducer 122 and serves to modify the current flow in the device. Inthe preferred embodiment of the speed control circuit a N-P-N transistor186 is used as the current control device. That transistor's collectoris attached to the Hall transducer and by modification of the basevoltage appearing on the transistor current flow through the Hall devicecan be increased and decreased. By increasing the current flow greateramplitude of oscillation are achieved and conversely a decrease in thecurrent flow in the Hall device results in lower amplitude ofoscillation.

To produce variations in the Hall current the speed control circuit 118includes two inputs 182, 183 which modify the N-P-N base voltage andthereby alter the Hall current flowing in the device. A first input 182is a control voltage from a control module and can be varied by the userto modify the base voltage. The second input 183 is also adjustable andprovides a low signal adjustment which is added to the first input at asumming junction 187. The speed control 118 further comprises twoamplifiers 184, 185 which transmit the inputs 182, 183 to the base ofthe N-P-N transistor.

From the above it should be apparent that the input 170 to thecomparator 150 is a signal whose size depends not only on a desiredspeed or amplitude of the oscillation but also on the actual amplitudeof oscillation as measured by the Hall transducer. Modifications of thesignal 170 therefore occur in response to changes in the load in thefeeder bowl as well as to changes introduced by the user throughmodification of the two speed control inputs 182, 183. In this way anamplitude sensing circuit control is employed which accurately producesa control signal dependent upon the amplitude of vibration even forsmall amplitudes which posed a problem for prior art amplitude sensingcircuitry.

The comparator 150 compares its two input signals and produces anoutput. The comparator is configured such that when the input 168 fromthe sawtooth generator is greater than the input 170, the output 144from the comparator will be high and current may pass through theoptically coupled SCR 138. Conversely, whenever the input 168 is lowerthan the input 170, the output 144 will be low and the optically coupledSCR will not conduct. Thus when the sawtoothed waveform reaches avoltage above the waveform from the amplitude sensing circuit, thecomparator 150 produces a high level output and the optically coupledSCR 138 sends a gating signal to the bowl drive SCR 130. This gatingsignal renders the bowl drive SCR 130 conductive, and the 120 voltalternating current source energizes the bowl coil and vibrates thebowl.

When the sawtoothed waveform drops below the amplitude sensing circuitwaveform, the comparator 150 produces a low output and the opticallycoupled SCR is turned off. The gating signal to the bowl drive SCR 130stops and the 120 volt alternating current source 113 no longerenergizes the bowl coil. The affect of the comparison made by thecomparator 150 is to render conductive the optically coupled SCR 138during selective portions of the sawtooth waveform. Thus, if thesawtooth 168 is greater than the amplitude signal 170 for only a smallportion of the alternating current cycle, the bowl coil will beenergized for a short time and little power applied to the bowl. If thesawtooth 168 exceeds the amplitude signal 170 for a greater portion ofthe cycle, more power drives the feeder bowl.

As the load within the bowl changes, the portion of the AC cycle duringwhich the bowl coil is energized varies to maintain constant amplitudevibrations. When a large number of parts are dumped from the supplyhopper 16 to the vibratory bowl 20, the bowl must be driven with morepower to achieve constant amplitude oscillation. This is achieved sincethe input 170 from the amplitude sensing circuit is lowered and thesawtooth waveform is greater than the output 170 for a longer timeperiod which renders the optically coupled SCR 138 conductive for alonger time period. As this greater power achieves a larger ampitude,the amplitude signal 170 again increases and the time of conductionagain decreases until a uniform amplitude of oscillation is achieved.

When the control voltage 119 is low, the first optically coupled SCR 138stops gating the drive SCR and the braking circuit 114 begins to sendsignals to the power circuit to affirmatively damp the bowl mechanism.To achieve this damping, a braking SCR 132 allows current to flowthrough the bowl mechanism in a direction opposed to the positive bowldrive. When the brake SCR 132 is rendered conductive, therefore, asignal passes through the bowl coil which sets up electromagneticinteractions between the I and E laminations and damps motion of thefeeder bowl 20.

The braking circuit 114 has two outputs 160, 148. The effect the output160 has upon the comparator 152 has been described. The output 148controls conduction of the second optically coupled SCR 140. When thecontrol voltage 119 goes low, the output 146 of the midpoint comparatorautomatically goes high eliminating the possibility of conduction of thefirst optically coupled SCR 138 and permitting the second opticallycoupled SCR 140 to conduct depending upon the voltage level of theoutput 148.

During the time period in which the control voltage 119 is high and thebowl is being driven, the signal 160 passes to a capacitor 190 by meansof diode 191. The diode 191 allows this signal to charge the capacitor190 to a value of about 10 volts.

The voltage on the capacitor 190 forms the output 149 which istransmitted to the inverting input of a comparator amplifier 154. Thenon-inverting input 194 is connected to a variable voltage divider 196which provides a means for adjusting the voltage on this non-invertinginput. So long as the voltage 149 on the inverting input is greater thanthe non-inverting input the output 148 from this amplifier 154 is low.

Once the control voltage 119 goes low, however, the capacitor 190 beginsto discharge since the contral voltage 119 is no longer maintaining itscharge. This discharge is achieved through a resistor 198 connectedbetween the output of the capacitor and ground. This discharge willcontinue until the voltage from the capacitor at the inverting input 149becomes less than the voltage maintained on the noninverting input 194due to action of the variable voltage divider 196. Throughout this timeperiod of capacitor discharge, the output 148 is maintained in a lowlevel. The input 146, however, to the power circuit is maintained at ahigh level once the control voltage goes low. During the time therefore,that the capacitor 190 is discharging, current is allowed to flowthrough the optically coupled SCR 140 which sends a gating signal 136 tothe braking SCR 132. As long as the capacitor voltage output is abovethe reference voltage 194, a gating signal will appear at the SCR andthe bowl coil can be driven in an opposed direction due to operation ofthat SCR. This bowl braking occurs in a sense opposite to the previousbowl drive and therefore damps oscillations due to the inertia and theless than optimum damping force provided by the leaf springs.

The values of the capacitor 190 and resistor 198 determine a timeconstant indicative of how long it takes the capacitor 190 to dischargethat amount. By changing these discrete component values or adjustingthe variable potential divider 196, it is possible for the user to "finetune" the braking action of the apparatus.

In this regard it should be appreciated that if the braking signal isallowed to flow through the bowl coil too long a period of time, abraking action will occur but at some point the bowl will again bedriven by the power source 113. For this reason the voltage divider 196must be adjusted to allow the comparator output 148 to be at a low levelfor only an appropriate period of time, neither too short to effectivelybrake nor too long to overdrive the system.

To more completely appreciate the combined amplitude sensing and speedcontrol achieved through utilization of the "Hall Effect" transducer itis instructive to examine the voltage wave forms at selective junctionsof the control circuit 110. FIGS. 8A-8E show waveforms for two differentamplitudes of bowl vibration. The solid line in these figurescorresponds to voltage wave forms which provide an oscillation ofapproximately 0.075 inches of peak to peak bowl vibration. The dottedline corresponds to wave forms which provide an oscillation ofapproximately 0.125 inches of peak to peak bowl vibration.

FIG. 8A illustrates the voltage difference across the two Hall Effecttransducer outputs as a function of time. These inputs are sent to theamplifier 172 for transmission to the other pulse forming componentswithin the circuitry. All other wave forms (8B-8E) are shown onidentical time bases. The output from the Hall Effect transducerdiminishes for increased bowl vibration. The peak voltage output fromthe Hall Effect transducer remains at approximately 6 volts for allamplitudes but as vibration amplitudes increase the minimum voltage onthe Hall Effect transducer waveform decreases. As noted previously thiswave form is amplified by the amplifier 172 and transmitted to thecomparator 174.

The output from the comparator 174 is illustrated in FIG. 8B. The waveform illustrated corresponds to an output in which a reference invertinginput 177 to the comparator 174 is set at approximately 5.9 volts.Whenever the Hall Effect amplifier output exceeds this 5.9 volt settingthe comparator amplifier 174 produces an output of approximately 9volts. Thus as the Hall Effect output decreases the comparator amplifieroutput also decreases due to the fact that the Hall transducer output isgreater than the reference voltage for a smaller period of time. Thecomparator pulse width for the 0.075 inch vibration (solid line) isapproximately 2 milliseconds and the pulse width for the 0.125 inchvibration (dotted line) is approximately 1 millisecond.

The output from the comparator amplifier 174 is integrated by anintegrator 176 and transmitted to the inverting input of an amplifier150. This integrated wave form appears in FIG. 8C as a sharply risingvoltage followed by a more gradually sloping decrease in voltage. Theincreasing portion of the wave form has approximately the same slope forboth the small and large amplitudes of vibration but the integratedwaveform for the large amplitude results in a more gradually slopingdecrease in integrated signal from a peak voltage substantially lessthan the waveform for the small amplitude of oscillation.

The integrated wave form is compared to a sawtooth wave form which isillustrated in FIG. 8D. As noted above, the output from the comparator150 is high whenever the sawtooth wave form (FIG. 8D) is greater thanthe integrated wave form. Since the sawtooth wave form is constant inshape and amplitude it is modulation of the integrated wave form whichresults in different outputs from the comparator 150. As the integratedwave form decreases (corresponding to an increase in amplitude) thesawtooth is greater than the integrated wave form for a longer period oftime and therefore the comparator output 144 is high for a greaterduration therefore rendering conductive the drive SCR 130 for a longertime period. The increase in conduction of this drive SCR 130 results ina greater amplitude of oscillation as desired. For a low amplitude ofoscillation (solid line in FIGS. 8A-E) the integrated wave form issubstantially larger and the comparison between it and the sawtooth waveform results in a shorter duration of on time for the comparator output.In FIG. 8E the 0.075 inch amplitude is produced by an on time per cycleof approximately 11 milliseconds and the 0.125 inch amplitude by an ontime per cycle of approximately 13 milliseconds.

It is apparent from FIGS. 8A-E that by adjusting the Hall amplitudeoutput through modification of the speed input it is possible thereforeto selectively control the time period in which the drive SCR isrendered conductive. Changes in load produce changes which also causethe comparator 150 to temporarily change the gating of the drive SCR 130until such changes again cause the system to reach an equilibriumvibration condition.

While the unique and novel material handling apparatus and brakingsystem have been described with particularity, it should be appreciatedthat certain modifications could be incorporated without departing fromthe spirit or scope of the invention as set forth in the appendedclaims.

What is claimed is:
 1. A vibratory feeder comprising:(a) a feederelement mounted for vibratory motion relative to a fixed base, saidelement comprising mechanical structure for feeding articles therefromin response to vibratory motion of said element; (b) electromagneticpower means coupled to vibrate the feeder element at a frequency whichis a function of an AC line frequency couplable to the power means; and(c) a braking control circuit coupled to the power means for, inresponse to occurrence of a stop command, causing the power means toapply energy from the line to the element in pulses at approximatelysaid vibration frequency and timed to actively counteract continuedvibratory movement.
 2. The vibratory feeder of claim 1, where:said powermeans comprises an AC motor coupled to vibrate said feeder element atsubstantially the alternating current line frequency.
 3. A vibratoryfeeder comprising:(a) a receptacle mounted for vibratory motion and forholding articles to be fed from the receptacle in response to thevibratory motion; (b) an electric driver couplable to an AC power sourceto apply force to the receptacle in synchrony with the line frequencyfor vibrating the receptacle at a steady state frequency which is afunction of the alternating line frequency applied to the driver; (c) areference generator for producing a periodic time varying referencesignal representing said steady state frequency and a referencevibration amplitude; (d) a detector system for producing a waveformwhich is a function of actual frequency of receptacle vibration, actualphase and amplitude of such vibration, and an independently variablepredetermined amplitude of vibration of the receptacle; (e) powercontrol circuitry including comparator circuitry coupled between thedetector, reference generator and the driver and comprising:(i)circuitry responsive to the detector and reference generator for causingthe driver to apply power in a relatively high range to increasevibratory motion of the receptacle when one of said detected frequencyand amplitude of vibration is less than said steady state frequency andpredetermined amplitude, respectively, and (ii) circuitry responsive tosaid detector and said reference generator for reducing the powerapplied by the driver to vibrate the receptacle when the amplitude andfrequency of receptacle vibration reach said predetermined amplitude andsteady state frequency, respectively.
 4. The vibratory feeder of claim3, wherein:said detector comprises a Hall effect transducer and a magnetaffixed to the receptacle for cooperatively sensing instantaneousmechanical displacement of at least a portion of said receptacle at apredetermined portion of the receptacle.
 5. A vibratory feeder apparatuscomprising:(a) a feeder element for guiding movement of articles thereinin response to vibration of the feeder element; (b) electromagneticdrive means coupled to said feeder and responsive to application ofelectric drive energy from a line to impart vibration to said element,and (c) braking means including circuitry responsive to furtherapplication of electric drive energy for causing the drive means toapply power in pulses from the line to actively oppose vibration of thefeeder element in substantial synchrony against such vibration.
 6. Thefeeder of claim 5, wherein:(a) said drive means is couplable to analternating source of line energy, and (b) said braking means comprisescircuitry for applying braking force to the feeder element in synchronywith the alternating line energy.
 7. A vibratory feeder apparatuscomprising:(a) a feeder element for feeding articles therefrom inresponse to vibratory motion of the feeder element; (b) electromagneticdrive means coupled to the feeder element and couplable to analternating current electrical power line for applying power fromsubstantially only one polarity of half cycles of said alternatingelectric line energy for vibrating the feeder element, and (c) brakingcircuitry including gating means coupled to the electromagnetic drivemeans for applying braking power from the line to oppose vibration ofthe feeder element, said power being drawn from substantially only thoseAC half cycles having a polarity opposite the polarity of the halfcycles utilized in vibrating the feeder element.
 8. A method ofvibratory feeding comprising the steps of:(a) vibrating a feeder elementsubstantially synchronously with alternating current power from a line,and (b) in response to the occurrence of a stop command signal, applyingenergy from the alternating current line in pulses synchronous with theAC line frequency for opposing actively continued vibratory movement ofthe feeder element.
 9. A method of vibratory feeding comprising thesteps of:(a) applying force to a feeder receptacle in synchrony with theline frequency of an AC power source for vibrating the receptacle at asteady state frequency which is a function of the alternating linefrequency applied to drive the receptacle; (b) producing a referencesignal representing said steady state frequency and a referencevibration amplitude; (c) producing a waveform which is a function ofactual frequency of receptacle vibration, actual phase and amplitude ofsuch vibration and an independently variable predetermined amplitude ofvibration of the receptacle; (d) causing, in response to comparison ofsaid waveform and said reference signal, the application of power in arelatively high range to increase vibratory motion of the receptaclewhen one of said actual frequency and amplitude of vibration is lessthan said steady state frequency and predetermined amplitude,respectively, and (e) in response to further comparison of saidreference signal and said waveform, reducing the power applied tovibrate the receptacle when the amplitude and frequency of receptaclevibration reach said predetermined amplitude and steady state frequency,respectively.
 10. A vibratory feeder comprising:(a) a receptacle mountedfor vibratory motion and having structure for holding articles to be fedtherefrom in response to vibratory motion of the receptacle; (b) drivemeans for vibrating the receptacle; (c) a detector coupled to thereceptacle comprising:(i) circuitry for producing a signal indicatinginstantaneous displacement of at least a portion of the receptacle withrespect to a predetermined location; (ii) circuitry for differentiatingand integrating said instantaneous displacement signal for producing awaveform indicating both actual amplitude and frequency of receptaclevibration, and (iii) circuitry for adjusting the amplitude of saidwaveform, and (d) control circuitry responsive to the detector forcontrolling operation of the motor.